Cotton Stalk-Derived Ferromagnetic Activated Carbon as an Efficient Fenton Catalyst for Cochineal Red Dye Degradation: Optimization and Kinetic Study

This study aims to synthesize activated carbon (ACGH) and ferromagnetic activated carbon (ACGH-Fe 3 O 4 ) derived from cotton stalks ( Gossypium herbaceum ) and to evaluate their catalytic performance in the degradation of Cochineal Red A (E124) dye in aqueous solution using the heterogeneous Fenton process. The textural, structural, and chemical properties of the synthesized materials were characterized using different analytical techniques. The degradation of E124 was investigated by varying several operational parameters, including the pH of the solution (3–7), hydrogen peroxide concentration (0.5–1.5 mol.L -1 ), initial dye concentration (100–200 mg.L -1 ), and catalyst dosage (50–100 mg). FTIR analysis of ACGH-Fe 3 O 4 confirmed the presence of Fe-O functional groups, while X ray diffraction analysis revealed the formation of a magnetite crystalline structure. The specific surface areas of ACGH and ACGH-Fe 3 O 4 were determined to be approximately 694.35 and 287.14 m 2 .g -1 , respectively, indicating the presence of micro and mesoporous structures. Catalytic performance tests showed that the degradation efficiencies of Fe 3 O 4 , ACGH, and ACGH-Fe 3 O 4 reached 35.32%, 51.56%, and 99.95%, respectively, after 60 min of reaction. Process optimization using response surface methodology (RSM) based on the Box–Behnken design (BBD) confirmed a maximum degradation efficiency of 99.97% at an optimal catalyst dosage of 1.5 g.L -1 . The quadratic regression model provided coefficients of determination of R 2 = 0.9217 and adjusted R 2 = 0.8488, indicating good agreement between the experimental and predicted values. Kinetic analysis revealed that the degradation of E124 follows a pseudo-first-order model. In addition, the ACGH-Fe 3 O 4 catalyst exhibited good reusability, maintaining degradation efficiencies between 90% and 70% after five successive cycles. Compared to conventional activated carbons, ACGH-Fe 3 O 4 demonstrated superior catalytic efficiency, fast kinetics, and excellent reusability, highlighting its potential for practical wastewater treatment.